Bradley Ambrose says he unwittingly recorded the conversation between National Party leader John Key and ACT's John Banks.

He then handed it to the Herald on Sunday newspaper.
His lawyer, Ron Mansfield, says the legal action is being taken in the light of the allegations being made publicly against his client that his conduct was criminal or unethical.

Mr Mansfield says Mr Ambrose's reputation is important because journalism is his sole source of income and he is being used by a political party for its gain.